DGNSS

DGNSS (differential global navigation satellite system) is GNSS positioning corrected by a fixed reference station of known coordinates, which computes the error in the satellite signals and broadcasts a correction to nearby receivers. It cuts the standalone GNSS error from roughly 5 to 10 m to about 1 to 3 m, enough for harbor approach, dredging control, and hydrographic survey. The marine maritime DGNSS service transmits corrections in the 283.5 to 325 kHz medium-frequency radiobeacon band using the RTCM SC-104 message format, with IALA coordinating the network. DGPS is the GPS-only case. Survey-grade real-time kinematic (RTK) and satellite-based augmentation (SBAS) give centimeter to sub-meter accuracy beyond basic DGNSS.